The loss of immune tolerance characterizes the airway inflammation seen in asthma and allergy. This immune dysregulation has been attributed to reduced numbers and function of regulatory T-cells, including FoxP3+ regulatory T-cells (Treg) and IL-10 producing TR1. Strategies to promote their numbers and function would have great therapeutic benefit. Both Treg and TR1 require signaling through the IL-2R and the TCR for their induction and maintenance. However, the availability of IL-2 is tightly regulated and exposure to cognate antigens is often intermittent. Mechanisms that support regulatory T-cells in settings of low IL-2 and low cognate antigen are therefore crucial to immune homeostasis. The PI has identified roles for the extracellular matrix molecule hyaluronan (HA) and its receptor CD44 in promoting the number and function of regulatory T-cells. CD44 crosslinking in the setting of low-dose antigen promotes the function and maintenance of Foxp3+ Treg. The same cues also promote the induction of TR1 from conventional T-cell precursors. Building on this finding, intra-nasal delivery of low dose antigen and HMW- HA was used to induce antigen-specific TR1 in vivo. These responses are mediated through synergistic effects on IL-2R and TCR signaling. Because high molecular weight HA (HMW-HA) but not low molecular weight HA (LMW-HA) is capable of crosslinking CD44, tissue integrity plays a decisive role in these effects. In Aims 1 and 2 the PI proposes to investigate the natural role of HMW-HA in Treg homeostasis. In Aim 3 the PI will evaluate whether TR1 induced using intra-nasal vaccination with a HMW-HA adjuvant can prevent inflammation in an antigen-specific mouse model of airway hypersensitivity. This is a novel and highly innovative approach to immune modulation with great potential for the prevention of asthma and allergy.